In the big and highly complex modern warehouses in which, in many cases, millions of dollars worth of goods and articles are stored, it has been conventional practice to store the articles on pallets which are arranged in vertical columns, floor to ceiling. To effect efficiency of space use, the columns are often placed so close together that there is little or no space between them to form an air passage. Further, even if there is a passage forming space between adjacent pallet load columns, because the columns are created by stacking a number of pallets, one above the other, if any one of the pallets is offset to the side of the column in which it is positioned, it can obstruct the passage between the sides of adjacent columns of stacked, loaded pallets. To conserve space and reduce overhead, the operators who stack and unstack the loaded pallets have a strong incentive to arrange the columns of stacked pallets as close to each other as they can. Add to this that warehouses are frequently under pressure to make maximum use of their floor space both to accommodate the demand and to obtain the best return on the investment in warehouse space. Another contributing factor can be gradual deforming of the loads on the pallets, eventually resulting in restriction or closure of the space between adjacent columns of stacked palletized articles.
This has been found to be a serious deficiency in modern warehousing, particularly in the large, high ceiling warehouse wherein the columns of palletized stored articles are high. In each of these cases, the articles themselves become barriers to the movement of smoke from an incipient fire to a position near the ceiling where the presence of the smoke could be detected at a very early stage of a fire. As warehousing has become larger and more complex and the value of what is being stored has been increasing, the exposure has become an increasingly serious problem and, in some cases, an unacceptable financial risk. While the importance of early detection has long been recognized as a critical factor in controlling fire damage losses, the problem of providing dependable, early fire detection means in large, modern warehouses has not heretofore been solved. It has continued to be a situation in which the fire may well have progressed to a point where it is already well established before any type of alarm is given. This not only makes the problem of extinguishing the fire substantially more complicated, it also materially increases the extent of the damage even from a fire which, even at a relatively early stage, is extinguished. This invention is directed to providing a simple, dependable and relatively inexpensive solution to this problem.